Looking for more sharpness

Your combo should be much more than sharp enough for 11x17 prints. I assumed you were printing much larger. With good technique you'll get near per-pixel sharpness (and then smart sharpen in photoshop) at 300dpi. At 11X17 I'm surprised you have any issues whatsoever; that should be totally tack sharp with that combination. Larger and I'd consider full frame an improvement, but I've seen 30X40 or so prints from the 5D Mark I and II that were acceptable.

For portraiture I'd go longer than 35m or 50mm, though (though not for "environmental portraiture"). Although Martin Schoeller shoots 140mm on a 6x7 and gets good results and that's shorter than one would expect for portraiture. I like his style. Simple and tacky, but distinctive and expressive.

Full frame does give you better micro contrast for sure. If you like 50mm consider getting the 50mm f1.8 as a stop gap, though, as it's nice on full frame and APS-C. That is a very sharp lens (with poor bokeh, unfortunately). My favorite lens on my Mark III. But you'll have to strain very very hard to tell the difference between the 7D and 5D at 11X17 except for the shallower depth of field on the 5D at a given aperture and field of view. Just get some lights and control your light outside better (reflectors, butterflies, strobes, etc.); it sounds to me like sharpness isn't your problem. Being in a studio will make nothing any sharper, just better lit.